From 230bc2d04a5ca60a668c0e6409a4c150d8a14824 Mon Sep 17 00:00:00 2001
From: Jeremy Hu <huxingyi@msn.com>
Date: Sat, 17 Dec 2016 10:19:40 +0930
Subject: [PATCH] Add draw cylinder

---
 README.md        |  7 +++--
 src/drawcommon.h |  1 +
 src/drawsphere.h |  1 +
 src/glwidget.cpp | 74 ++++++++++++++++++++++++++++++++++++++++++++++--
 4 files changed, 79 insertions(+), 4 deletions(-)

diff --git a/README.md b/README.md
index df4670c9..6639a320 100644
--- a/README.md
+++ b/README.md
@@ -11,7 +11,10 @@ From my initial thought, Dust3D should be a tool like [Makehuman](http://www.mak
 
 Progress
 ==============
-Drawing Sphere
+Drawing Primitives
 -----------
+*Sphere*  
 I don't want the whole project have any unnecessary dependent, like glu library.
-Let's start with [drawing a sphere without gluSphere]( http://stackoverflow.com/questions/7687148/drawing-sphere-in-opengl-without-using-glusphere), because I want implement the same balls which presented in the [B-Mesh paper](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.357.7134&rep=rep1&type=pdf).  
+Let's start with [drawing a sphere without gluSphere]( http://stackoverflow.com/questions/7687148/drawing-sphere-in-opengl-without-using-glusphere), because I want implement the same balls which presented in the [B-Mesh paper](http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.357.7134&rep=rep1&type=pdf).   
+*Cylinder*  
+Two caps and many strips composites a cylinder.
diff --git a/src/drawcommon.h b/src/drawcommon.h
index 10cb6167..befdacc5 100644
--- a/src/drawcommon.h
+++ b/src/drawcommon.h
@@ -23,6 +23,7 @@ typedef struct {
 void normalize(point *p);
 void midpoint(point *a, point *b, point *mid);
 void drawTriangle(triangle *poly);
+int drawCylinder(int slices, float radius, float height);
 
 #ifdef __cplusplus
 }
diff --git a/src/drawsphere.h b/src/drawsphere.h
index 839dde5f..3d6a9929 100644
--- a/src/drawsphere.h
+++ b/src/drawsphere.h
@@ -1,5 +1,6 @@
 #ifndef DRAW_SPHERE_H
 #define DRAW_SPHERE_H
+#include "drawcommon.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/src/glwidget.cpp b/src/glwidget.cpp
index f2167858..797cc18b 100644
--- a/src/glwidget.cpp
+++ b/src/glwidget.cpp
@@ -1,6 +1,7 @@
 #include <QtGui>
 #include <QtOpenGL>
 #include <assert.h>
+#include <math.h>
 #include "glwidget.h"
 #include "drawcommon.h"
 #include "drawsphere.h"
@@ -16,8 +17,71 @@ void drawTriangle(triangle *poly) {
   glEnd();
 }
 
+int drawCylinder(int slices, float radius, float height) {
+  float theta = (2.0 * M_PI) / (float)slices;
+  float a = 0.0f;
+  int lv;
+  float halfHeight = height / 2;
+  float x, y, z;
+
+  if (slices <= 0) {
+    fprintf(stderr, "%s:Invalid parameter(slices:%d).\n", __FUNCTION__, slices);
+    return -1;
+  }
+
+  // bottom cap
+  z = -halfHeight;
+  glBegin(GL_TRIANGLE_FAN);
+  glNormal3f(0, 0, -1);
+  glVertex3f(0, 0, z);
+  for (a = 0, lv = 0; lv <= slices; ++lv) {
+    x = cos(a) * radius;
+    y = sin(a) * radius;
+    glNormal3f(0, 0, -1);
+    glVertex3f(x, y, z);
+    a += theta;
+  }
+  glEnd();
+
+  // top cap
+  z = halfHeight;
+  glBegin(GL_TRIANGLE_FAN);
+  glNormal3f(0, 0, 1);
+  glVertex3f(0, 0, z);
+  for (a = 0, lv = 0; lv <= slices; ++lv) {
+    x = cos(a) * radius;
+    y = sin(a) * radius;
+    glNormal3f(0, 0, 1);
+    glVertex3f(x, y, z);
+    a += theta;
+  }
+  glEnd();
+
+  // strips
+  glBegin(GL_TRIANGLE_STRIP);
+  for (a = 0, lv = 0; lv <= slices; ++lv) {
+    float cosa = cos(a);
+    float sina = sin(a);
+    x = cosa * radius;
+    y = sina * radius;
+    z = -halfHeight;
+    glNormal3f(cosa, sina, 0);
+    glVertex3f(x, y, z);
+    z = halfHeight;
+    glNormal3f(cosa, sina, 0);
+    glVertex3f(x, y, z);
+    a += theta;
+  }
+  glEnd();
+
+  return 0;
+}
+
 GLWidget::GLWidget(QWidget *parent)
-  : QGLWidget(QGLFormat(QGL::SampleBuffers), parent) {
+    : QGLWidget(QGLFormat(QGL::SampleBuffers), parent) {
+  QTimer *timer = new QTimer(this);
+  connect(timer, SIGNAL(timeout()), this, SLOT(update()));
+  timer->start(100);
 }
 
 GLWidget::~GLWidget() {
@@ -47,8 +111,14 @@ void GLWidget::initializeGL() {
 }
 
 void GLWidget::paintGL() {
+  static int angle = 0;
   glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
-  drawSphere(3);
+  //drawSphere(3);
+  glPushMatrix();
+  glRotatef(angle, 1, 0, 0);
+  angle = (angle + 1) % 360;
+  drawCylinder(50, 0.2, 2);
+  glPopMatrix();
 }
 
 void GLWidget::resizeGL(int w, int h) {